Changes in Root Cap pH Are Required for the Gravity Response of the Arabidopsis Root

• Published in: The Plant cell Vol. 13; no. 4; pp. 907 - 921
• Main Authors: Fasano, Jeremiah M., Swanson, Sarah J., Blancaflor, Elison B., Dowd, Peter E., Kao, Teh-hui, Gilroy, Simon
• Format: Journal Article
• Language: English
• Published: Legacy CDMS American Society of Plant Physiologists 01-04-2001; American Society of Plant Biologists
• Subjects: Arabidopsis - growth & development; Arabidopsis - physiology; Cell growth; Cell Wall - physiology; Cell walls; Cellulose; Dextrans; Fluoresceins; Fluorescent Dyes; Gravitropism; Gravity Sensing; Hydrogen-Ion Concentration; Kinetics; Life Sciences (General); Meristem - growth & development; Meristem - physiology; Microscopes; Microscopy, Confocal; pH sensors; Plant roots; Plant Roots - growth & development; Plant Roots - physiology; Plants; Protons; Root cap; Space life sciences; Nasa Discipline Plant Biology; Non-Nasa Center; NASA Discipline Plant Biology; Non-NASA Center
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.13.4.907

Although the columella cells of the root cap have been identified as the site of gravity perception, the cellular events that mediate gravity signaling remain poorly understood. To determine if cytoplasmic and/or wall pH mediates the initial stages of root gravitropism, we combined a novel cell wall pH sensor (a cellulose binding domain peptide-Oregon green conjugate) and a cytoplasmic pH sensor (plants expressing pH-sensitive green fluorescent protein) to monitor pH dynamics throughout the graviresponding Arabidopsis root. The root cap apoplast acidified from pH 5.5 to 4.5 within 2 min of gravistimulation. Concomitantly, cytoplasmic pH increased in columella cells from 7.2 to 7.6 but was unchanged elsewhere in the root. These changes in cap pH preceded detectable tropic growth or growth-related pH changes in the elongation zone cell wall by 10 min. Altering the gravity-related columella cytoplasmic pH shift with caged protons delayed the gravitropic response. Together, these results suggest that alterations in root cap pH likely are involved in the initial events that mediate root gravity perception or signal transduction.